I, too, have a Samsung Galaxy J3 but have never experienced a blue bubble beeping at the bottom of my screen. I’d guess it’s one of your apps trying to alert you to something. If you swipe down from the top of your screen, do you see any notifications? Might the bubble look like this:

If so, that’s the Android Messages icon and your phone might be alerting you to a received text message.

If not, perhaps, you might capture and post a screenshot for us. To capture that screenshot, press the power button and home button simultaneously until you hear a click, then release both buttons.